Synthesis of functionalized high vinyl rubber

ABSTRACT

This invention is based upon the discovery that rubbery polymers having a high vinyl content and a low degree of branching can be synthesized with an initiator system that is comprised of (a) a lithium initiator selected from the group consisting of allylic lithium compounds and benzylic lithium compounds, (b) a Group I metal alkoxide, and (c) a polar modifier; wherein the molar ratio of the Group I metal alkoxide to the polar modifier is within the range of about 0.1:1 to about 10:1; and wherein the molar ratio of the Group I metal alkoxide to the lithium initiator is within the range of about 0.01:1 to about 20:1. These high vinyl polymers offer reduced levels of hysteresis and better functionalization efficiency. By virtue of their lower level of hysteresis these polymers can be utilized in manufacturing tire tread compounds that exhibit lower levels of rolling resistance and can accordingly be used to improve the fuel economy of motor vehicles without compromising other desirable characteristics, such as traction and tread-wear.

This patent application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/436,923, filed on Dec. 27, 2002.

BACKGROUND OF THE INVENTION

It is highly desirable for tires to exhibit good tractioncharacteristics on both dry and wet surfaces. However, it hastraditionally been very difficult to improve the tractioncharacteristics of a tire without compromising its rolling resistanceand tread wear. Low rolling resistance is important because good fueleconomy is virtually always an important consideration. Good tread wearis also an important consideration because it is generally the mostimportant factor that determines the life of the tire.

The traction, tread wear, and rolling resistance of a tire is dependentto a large extent on the dynamic viscoelastic properties of theelastomers utilized in making the tire tread. In order to reduce therolling resistance of a tire, rubbers having a high rebound havetraditionally been utilized in making the tire's tread. On the otherhand, in order to increase the wet skid resistance of a tire, rubberswhich undergo a large energy loss have generally been utilized in thetire's tread. In order to balance these two viscoelasticallyinconsistent properties, mixtures of various types of synthetic andnatural rubber are normally utilized in tire treads. For instancevarious mixtures of styrene-butadiene rubber and polybutadiene rubberare commonly used as a rubber material for automobile tire treads.However, such blends are not totally satisfactory for all purposes.

The inclusion of styrene-butadiene rubber (SBR) in tire treadformulations can significantly improve the traction characteristics oftires made therewith. However, styrene is a relatively expensive monomerand the inclusion of SBR is tire tread formulations leads to increasedcosts.

Carbon black is generally included in rubber compositions that areemployed in making tires and most other rubber articles. It is desirableto attain the best possible dispersion of the carbon black throughoutthe rubber to attain optimized properties. It is also highly desirableto improve the interaction between the carbon black and the rubber. Byimproving the affinity of the rubber compound to the carbon black,physical properties can be improved. Silica can also be included in tiretread formulations to improve rolling resistance.

U.S. Pat. No. 4,843,120 discloses that tires having improved performancecharacteristics can be prepared by utilizing rubbery polymers havingmultiple glass transition temperatures as the tread rubber. Theserubbery polymers having multiple glass transition temperatures exhibit afirst glass transition temperature which is within the range of about−110° C. to −20° C. and exhibit a second glass transition temperaturewhich is within the range of about −50° C. to 0° C. According to U.S.Pat. No. 4,843,120, these polymers are made by polymerizing at least oneconjugated diolefin monomer in a first reaction zone at a temperatureand under conditions sufficient to produce a first polymeric segmenthaving a glass transition temperature which is between −110° C. and −20°C. and subsequently continuing said polymerization in a second reactionzone at a temperature and under conditions sufficient to produce asecond polymeric segment having a glass transition temperature which isbetween −20° C. and 20° C. Such polymerizations are normally catalyzedwith an organolithium catalyst and are normally carried out in an inertorganic solvent.

U.S. Pat. No. 5,137,998 discloses a process for preparing a rubberyterpolymer of styrene, isoprene, and butadiene having multiple glasstransition temperatures and having an excellent combination ofproperties for use in making tire treads which comprises:terpolymerizing styrene, isoprene and 1,3-butadiene in an organicsolvent at a temperature of no more than about 40° C. in the presence of(a) at least one member selected from the group consisting oftripiperidino phosphine oxide and alkali metal alkoxides and (b) anorganolithium compound.

U.S. Pat. No. 5,047,483 discloses a pneumatic tire having an outercircumferential tread where said tread is a sulfur cured rubbercomposition comprised of, based on 100 parts by weight rubber (phr), (A)about 10 to about 90 parts by weight of a styrene, isoprene, butadieneterpolymer rubber (SIBR), and (B) about 70 to about 30 weight percent ofat least one of cis 1,4-polyisoprene rubber and cis 1,4-polybutadienerubber wherein said SIBR rubber is comprised of (1) about 10 to about 35weight percent bound styrene, (2) about 30 to about 50 weight percentbound isoprene and (3) about 30 to about 40 weight percent boundbutadiene and is characterized by having a single glass transitiontemperature (Tg) which is in the range of about −10° C. to about −40° C.and, further the said bound butadiene structure contains about 30 toabout 40 percent 1,2-vinyl units, the said bound isoprene structurecontains about 10 to about 30 percent 3,4-units, and the sum of thepercent 1,2-vinyl units of the bound butadiene and the percent 3,4-unitsof the bound isoprene is in the range of about 40 to about 70 percent.

U.S. Pat. No. 5,272,220 discloses a styrene-isoprene-butadiene rubberwhich is particularly valuable for use in making truck tire treads whichexhibit improved rolling resistance and tread wear characteristics ,said rubber being comprised of repeat units which are derived from about5 weight percent to about 20 weight percent styrene, from about 7 weightpercent to about 35 weight percent isoprene, and from about 55 weightpercent to about 88 weight percent 1,3-butadiene, wherein the repeatunits derived from styrene, isoprene and 1,3-butadiene are inessentially random order, wherein from about 25% to about 40% of therepeat units derived from the 1,3-butadiene are of thecis-microstructure, wherein from about 40% to about 60% of the repeatunits derived from the 1,3-butadiene are of the trans-microstructure,wherein from about 5% to about 25% of the repeat units derived from the1,3-butadiene are of the vinyl-microstructure, wherein from about 75% toabout 90% of the repeat units derived from the isoprene are of the1,4-microstructure, wherein from about 10% to about 25% of the repeatunits derived from the isoprene are of the 3,4-microstructure, whereinthe rubber has a glass transition temperature which is within the rangeof about −90° C. to about −70° C., wherein the rubber has a numberaverage molecular weight which is within the range of about 150,000 toabout 400,000, wherein the rubber has a weight average molecular weightof about 300,000 to about 800,000, and wherein the rubber has aninhomogeneity which is within the range of about 0.5 to about 1.5.

U.S. Pat. No. 5,239,009 reveals a process for preparing a rubberypolymer which comprises: (a) polymerizing a conjugated diene monomerwith a lithium initiator in the substantial absence of polar modifiersat a temperature which is within the range of about 5° C. to about 100°C. to produce a living polydiene segment having a number averagemolecular weight which is within the range of about 25,000 to about350,000; and (b) utilizing the living polydiene segment to initiate theterpolymerization of 1,3-butadiene, isoprene, and styrene, wherein theterpolymerization is conducted in the presence of at least one polarmodifier at a temperature which is within the range of about 5° C. toabout 70° C. to produce a final segment which is comprised of repeatunits which are derived from 1,3-butadiene, isoprene, and styrene,wherein the final segment has a number average molecular weight which iswithin the range of about 25,000 to about 350,000. The rubbery polymermade by this process is reported to be useful for improving the wet skidresistance and traction characteristics of tires without sacrificingtread wear or rolling resistance.

U.S. Pat. No. 5,061,765 discloses isoprene-butadiene copolymers havinghigh vinyl contents which can reportedly be employed in building tireswhich have improved traction, rolling resistance, and abrasionresistance. These high vinyl isoprene-butadiene rubbers are synthesizedby copolymerizing 1,3-butadiene monomer and isoprene monomer in anorganic solvent at a temperature which is within the range of about −10°C. to about 100° C. in the presence of a catalyst system which iscomprised of (a) an organoiron compound, (b) an organoaluminum compound,(c) a chelating aromatic amine, and (d) a protonic compound; wherein themolar ratio of the chelating amine to the organoiron compound is withinthe range of about 0.1:1 to about 1:1, wherein the molar ratio of theorganoaluminum compound to the organoiron compound is within the rangeof about 5:1 to about 200:1, and herein the molar ratio of the protoniccompound to the organoaluminum compound is within the range of about0.001:1 to about 0.2:1.

U.S. Pat. No. 5,405,927 discloses an isoprene-butadiene rubber which isparticularly valuable for use in making truck tire treads, said rubberbeing comprised of repeat units which are derived from about 20 weightpercent to about 50 weight percent isoprene and from about 50 weightpercent to about 80 weight percent 1,3-butadiene, wherein the repeatunits derived from isoprene and 1,3-butadiene are in essentially randomorder, wherein from about 3% to about 10% of the repeat units in saidrubber are 1,2-polybutadiene units, wherein from about 50% to about 70%of the repeat units in said rubber are 1,4-polybutadiene units, whereinfrom about 1% to about 4% of the repeat units in said rubber are3,4-polyisoprene units, wherein from about 25% to about 40% of therepeat units in the polymer are 1,4-polyisoprene units, wherein therubber has a glass transition temperature which is within the range ofabout −90° C. to about −75° C., and wherein the rubber has a Mooneyviscosity which is within the range of about 55 to about 140.

U.S. Pat. No. 5,654,384 discloses a process for preparing high vinylpolybutadiene rubber which comprises polymerizing 1,3-butadiene monomerwith a lithium initiator at a temperature which is within the range ofabout 5° C. to about 100° C. in the presence of a sodium alkoxide and apolar modifier, wherein the molar ratio of the sodium alkoxide to thepolar modifier is within the range of about 0.1:1 to about 10:1; andwherein the molar ratio of the sodium alkoxide to the lithium initiatoris within the range of about 0.05:1 to about 10:1. By utilizing acombination of sodium alkoxide and a conventional polar modifier, suchas an amine or an ether, the rate of polymeriztion initiated withorganolithium compounds can be greatly increased with the glasstransition temperature of the polymer produced also being substantiallyincreased. The rubbers synthesized using such catalyst systems alsoexhibit excellent traction properties when compounded into tire treadformulations. This is attributable to the unique macrostructure (randombranching) of the rubbers made with such catalyst systems.

U.S. Pat. No. 5,620,939, U.S. Pat. No. 5,627,237, and U.S. Pat. No.5,677,402 also disclose the use of sodium salts of saturated aliphaticalcohols as modifiers for lithium initiated solution polymerizations.Sodium t-amylate is a preferred sodium alkoxide by virtue of itsexceptional solubility in non-polar aliphatic hydrocarbon solvents, suchas hexane, which are employed as the medium for such solutionpolymerizations. However, using sodium t-amylate as the polymerizationmodifier in commercial operations where recycle is required can lead tocertain problems. These problems arise due to the fact that sodiumt-amylate reacts with water to form t-amyl alcohol during steamstripping in the polymer finishing step. Since t-amyl alcohol forms anazeotrope with hexane, it co-distills with hexane and thus contaminatesthe feed stream.

U.S. Pat. No. 6,140,434 discloses a solution to the problem of recyclestream contamination. U.S. Pat. No. 6,140,434 is based upon thediscovery that metal salts of cyclic alcohols are highly effectivemodifiers that do not co-distill with hexane or form compounds duringsteam stripping which co-distill with hexane. Since the boiling pointsof these metal salts of cyclic alcohols are very high, they do notco-distill with hexane and contaminate recycle streams. Additionally,metal salts of cyclic alcohols are considered to be environmentallysafe. In fact, sodium mentholate is used as a food additive.

U.S. Pat. No. 6,140,434 specifically discloses a process for preparing arubbery polymer having a high vinyl content which comprises:polymerizing at least one diene monomer with a lithium initiator at atemperature which is within the range of about 5° C. to about 100° C. inthe presence of a metal salt of a cyclic alcohol and a polar modifier,wherein the molar ratio of the metal salt of the cyclic alcohol to thepolar modifier is within the range of about 0.1:1 to about 10:1; andwherein the molar ratio of the metal salt of the cyclic alcohol to thelithium initiator is within the range of about 0.05:1 to about 10:1.

SUMMARY OF THE INVENTION

The present invention is based upon the discovery that rubbery polymershaving a high vinyl content and a low degree of branching can besynthesized with an initiator system that is comprised of (a) a lithiuminitiator selected from the group consisting of allylic lithiumcompounds and benzylic lithium compounds, (b) a Group I metal alkoxide,and (c) a polar modifier; wherein the molar ratio of the Group I metalalkoxide to the polar modifier is within the range of about 0.1:1 toabout 10:1; and wherein the molar ratio of the Group I metal alkoxide tothe lithium initiator is within the range of about 0.01:1 to about 20:1.The key to the present invention is the use of an allylic lithiumcompound or a benzylic lithium compound in the initiator system.

These high vinyl polymers offer reduced levels of hysteresis and betterfunctionalization efficiency. By virtue of their lower level ofhysteresis these polymers can be utilized in manufacturing tire treadcompounds that exhibit lower levels of rolling resistance and canaccordingly be used to improve the fuel economy of motor vehicleswithout compromising other desirable characteristics, such as tractionand tread-wear.

The subject invention further discloses a process for preparing arubbery polymer having a high vinyl content which comprises:polymerizing at least one diene monomer with a lithium initiatorselected from the group consisting of allylic lithium compounds andbenzylic lithium compounds at a temperature which is within the range ofabout 5° C. to about 120° C. in the presence of a Group I metal alkoxideand a polar modifier, wherein the molar ratio of the Group I metalalkoxide to the polar modifier is within the range of about 0.1:1 toabout 10:1; and wherein the molar ratio of the Group I metal alkoxide tothe lithium initiator is within the range of about 0.05:1 to about 10:1.

The present invention also reveals a process for preparing high vinylpolybutadiene rubber which comprises: polymerizing 1,3-butadiene monomerwith a lithium initiator selected from the group consisting of allyliclithium compounds and benzylic lithium compounds at a temperature whichis within the range of about 5° C. to about 120° C. in the presence ofGroup I metal alkoxide and a polar modifier, wherein the molar ratio ofthe Group I metal alkoxide to the polar modifier is within the range ofabout 0.1:1 to about 10:1; and wherein the molar ratio of the Group Imetal alkoxide to the lithium initiator is within the range of about0.05:1 to about 10:1.

The subject invention further discloses a high vinyl polydiene rubberwhich is comprised of at least 50 percent repeat units that are of vinylmicrostructure based upon the total number of polydiene repeat units inthe rubbery polymer, wherein said high vinyl polybutadiene rubber has aweight average molecular weight of at least 300,000, wherein said highvinyl polybutadiene rubber has a monomodal polydispersity of at least1.2, and a ratio of radius of gyration to weight average molecularweight of greater than 0.078 nm·mol/kg, wherein the radius of gyrationis determined at the weight average molecular weight by multi anglelaser light scattering and wherein the weight average molecular weightis determined by multi angle laser light scattering.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of differential weight fraction versus molecularweight.

FIG. 2 a is bar diagrams showing the weight percent of additionalmonomer grafted after the metallation step at a TMEDA/Li ratio of 3/1.

FIG. 2 b is bar diagrams showing the weight percent of additionalmonomer grafted after the metallation step at a SMT/Li ratio of 0.1/1.

FIG. 2 c is bar diagrams showing the weight percent of additionalmonomer grafted after the metallation step at a TMEDA/SMT/Li ratio of3/0.1/1.

FIG. 3 is a bar diagram showing the weight percent of additional monomergrafted at temperatures of 65° C., 72° C., and 78° C.

FIG. 4 is a plot of RMS radius versus molar mass.

FIG. 5 is a plot of G′ or G″ versus frequency.

FIG. 6 is a plot of tan delta versus frequency.

DETAILED DESCRIPTION OF THE INVENTION

The rubbery polymers synthesized using the initiator systems of thisinvention can be made by the homopolymerization of a conjugated diolefinmonomer or by the copolymerization of a conjugated diolefin monomer witha vinyl aromatic monomer. It is, of course, also possible to makerubbery polymers by polymerizing a mixture of conjugated diolefinmonomers with one or more ethylenically unsaturated monomers, such asvinyl aromatic monomers. The conjugated diolefin monomers which can beutilized in the synthesis of rubbery polymers in accordance with thisinvention generally contain from 4 to 12 carbon atoms. Those containingfrom 4 to 8 carbon atoms are generally preferred for commercialpurposes. For similar reasons, 1,3-butadiene and isoprene are the mostcommonly utilized conjugated diolefin monomers. Some additionalconjugated diolefin monomers that can be utilized include2,3-dimethyl-1,3-butadiene, piperylene, 3-butyl-1,3-octadiene,2-phenyl-1,3-butadiene, and the like, alone or in admixture.

Some representative examples of ethylenically unsaturated monomers thatcan potentially be copolymerized into rubbery polymers using themodifiers of this invention include alkyl acrylates, such as methylacrylate, ethyl acrylate, butyl acrylate, methyl methacrylate and thelike; vinylidene monomers having one or more terminal CH₂═CH— groups;vinyl aromatics such as styrene, α-methylstyrene, bromostyrene,chlorostyrene, fluorostyrene and the like; α-olefins such as ethylene,propylene, 1-butene and the like; vinyl halides, such as vinylbromide,chloroethane (vinylchloride), vinylfluoride, vinyliodide,1,2-dibromoethene, 1,1-dichloroethene (vinylidene chloride),1,2-dichloroethene and the like; vinyl esters, such as vinyl acetate;α,β-olefinically unsaturated nitriles, such as acrylonitrile andmethacrylonitrile; α,β-olefinically unsaturated amides, such asacrylamide, N-methyl acrylamide, N,N-dimethylacrylamide, methacrylamideand the like.

Rubbery polymers which are copolymers of one or more diene monomers withone or more other ethylenically unsaturated monomers will normallycontain from about 50 weight percent to about 99 weight percentconjugated diolefin monomers and from about 1 weight percent to about 50weight percent of the other ethylenically unsaturated monomers inaddition to the conjugated diolefin monomers. For example, copolymers ofconjugated diolefin monomers with vinylaromatic monomers, such asstyrene-butadiene rubbers which contain from 50 to 95 weight percentconjugated diolefin monomers and from 5 to 50 weight percentvinylaromatic monomers, are useful in many applications. The level ofthe vinylaromatic monomer is such copolymers with more typically bewithin the range of about 5 weight percent to about 40 weight percentand will more typically be within the range of about 15 weight percentto about 35 weight percent.

Vinyl aromatic monomers are probably the most important group ofethylenically unsaturated monomers that are commonly incorporated intopolydienes. Such vinyl aromatic monomers are, of course, selected so asto be copolymerizable with the conjugated diolefin monomers beingutilized. Generally, any vinyl aromatic monomer which is known topolymerize with organolithium initiators can be used. Such vinylaromatic monomers typically contain from 8 to 20 carbon atoms. Usually,the vinyl aromatic monomer will contain from 8 to 14 carbon atoms. Themost widely used vinyl aromatic monomer is styrene. Some examples ofvinyl aromatic monomers that can be utilized include styrene,1-vinylnaphthalene, 2-vinylnaphthalene, á-methylstyrene,4-phenylstyrene, 3-methylstyrene and the like.

In one embodiment of this invention a functionalized monomer iscopolymerized into the high vinyl polydiene rubber. The functionalizedmonomer will typically be incorporated into the high vinyl rubber in anamount which is within the range of 0.1 phm (parts by weight per 100parts by weight of monomer) to about 10 phm. The functionalized monomerwill more typically be incorporated into the polymer at a level with iswithin the range of about 0.2 phm to about 5 phm. The functionalizedmonomer will preferably be incorporated into the polymer at a level withis within the range of about 0.3 phm to about 3 phm.

The functionzlized monomers that can be copolymerized into such highvinyl polydiene rubbers by utilizing the technique of this inventionhave a structural formula selected from the group consisting of

wherein R represents an alkyl group containing from 1 to about 10 carbonatoms or a hydrogen atom, and wherein R¹ and R² can be the same ordifferent and represent hydrogen atoms or a moiety selected from thegroup consisting of

wherein R³ groups can be the same or different and represent a memberselected from the group consisting of alkyl groups containing from 1 toabout 10 carbon atoms, aryl groups, allyl groups, and alklyoxy groupshaving the structural formula —(CH₂)_(y)—O—(CH₂)_(z)—CH₃, wherein yrepresents an integer from 1 to 10, wherein z represents an integer from1 to 10, wherein Z represents a nitrogen containing heterocycliccompound, wherein R⁴ represents a member selected from the groupconsisting of alkyl groups containing from 1 to about 10 carbon atoms,aryl groups, and allyl groups, and wherein x and represents an integerfrom 1 to about 10, and wherein n represents an integer from about 1 toabout 10, with the proviso that R1 and R2 can not both be hydrogenatoms;

wherein n represents an integer from 1 to about 10 and wherein mrepresents an integer from 1 to about 10, with the proviso that the sumof n and m is at least 4;

wherein n represents an integer from 1 to about 10, and wherein R and R′can be the same or different and represent alkyl groups containing fromabout 1 to about 10 carbon atoms;

wherein n represents an integer from 1 to about 10 and wherein mrepresents an integer from 4 to about 10;

wherein x represents an integer from about 1 to about 10, wherein nrepresents an integer from 1 to about 10 and wherein m represents aninteger from 1 to about 10, with the proviso that the sum of n and m isat least 4;

wherein R represents a hydrogen atom or an alkyl group containing from 1to about 10 carbon atoms, wherein n represents an integer from 1 toabout 10, and wherein m represents an integer from 1 to about 10, withthe proviso that the sum of n and m is at least 4; and

wherein n represents an integer from 0 to about 10, wherein m representsan integer from 1 to about 10, wherein x represents an integer from 1 toabout 10, and wherein y represents an integer from 1 to about 10.

In functionalized monomers where R1 and/or R2 represent groups of thestructural formula:

it is preferred for the R³ groups to represent hydrogen atoms or alkylgroups containing from 1 to 4 carbon atoms, and for x to represent aninteger from 1 to 4. In such functionalized monomers it is mostpreferred for the R³ groups to represent hydrogen atoms.

Such functionalized monomers can be synthesized by utilizing a techniquedescribed in U.S. patent application Ser. No. 10/247,243, filed on Sep.19, 2002. The teachings of U.S. patent application Ser. No. 10/247,243are incorporated herein by reference. For instance, functionalizedstyrene monomer can be synthesized by reacting a secondary amine withvinyl benzyl halide, such as vinyl benzyl chloride, in the presence of astrong base to produce the functionalized styrene monomer. Thisprocedure can be depicted as follows:

This reaction is typically conducted at a temperature that is within therange of about −20° C. to about 40° C., and is preferably conducted at atemperature which is within the range of about −10° C. to about 30° C.This reaction will most preferable be conducted at a temperature whichis within the range of about 0° C. to about 25° C. The strong base canbe selected from a large variety of organic or inorganic compounds.Examples of organic bases are aromatic and aliphatic amines, pyridines,such as triethylamine, aniline, and pyridine. Examples of suitableinorganic bases are the salts of weak mineral acids such has sodiumcarbonate, calcium carbonate, sodium hyrdroxide, calcium hydroxide, andaluminum hyrdoxide. After the reaction has been completed volatilecompounds are removed under reduced pressure yielding the product as aviscous residue.

Functionalized monomers that contain cyclic amines can also be made bythe same reaction scheme wherein a cyclic secondary amine is employed inthe first step of the reaction. This reaction scheme can be depicted asfollows:

The functionalized styrene monomers that can be used in the practice ofthis invention are typically of the structural formula:

wherein R represents an alkyl group containing from 1 to about 10 carbonatoms or a hydrogen atom, and wherein R¹ and R² can be the same ordifferent and represent hydrogen atoms or a moiety selected from thegroup consisting of

wherein R³ groups can be the same or different and represent a memberselected from the group consisting of alkyl groups containing from 1 toabout 10 carbon atoms, aryl groups, allyl groups, and alklyoxy groupshaving the structural formula —(CH₂)_(y)—O—(CH₂)_(z)—CH₃, wherein yrepresents an integer from 1 to 10, wherein z represents an integer from1 to 10, wherein Z represents a nitrogen containing heterocycliccompound, wherein R⁴ represents a member selected from the groupconsisting of alkyl groups containing from 1 to about 10 carbon atoms,aryl groups, and allyl groups, and wherein x and represents an integerfrom 1 to about 10, and wherein n represents an integer from about 1 toabout 10, with the proviso that R¹ and R² can not both be hydrogenatoms. In these monomers R will typically represent a hydrogen atom or amethyl group, and x will typically represent an integer from 1 to 4. Inmost cases x will be 1. In one embodiment of this invention, R3 and R4can represent alkyl groups that contain from 1 to about 4 carbon atoms,aryl groups that contain from about 6 to about 18 carbon atoms, or allylgroups that contain from about 3 to about 18 carbon atoms.

Functionalized styrene monomers of the following structural formulas:

wherein n represents an integer from 4 to about 10 are highly useful inthe practice of this invention. In these functionalized styrene monomersn will normally represents 4 or 6.

The nitrogen containing heterocyclic group (Z group) will normally beone of the following moieties:

wherein R⁵ groups can be the same or different and represent a memberselected from the group consisting of alkyl groups containing from 1 toabout 10 carbon atoms, aryl groups, allyl groups, and alkoxy groups, andwherein Y represents oxygen, sulfur, or a methylene group.

Some representative examples of rubbery polymers which can besynthesized in accordance with this invention include polybutadiene,polyisoprene, styrene-butadiene rubber (SBR), α-methylstyrene-butadienerubber, α-methylstyrene-isoprene rubber, styrene-isoprene-butadienerubber (SIBR), styrene-isoprene rubber (SIR), isoprene-butadiene rubber(IBR), á-methylstyrene-isoprene-butadiene rubber andα-methylstyrene-styrene-isoprene-butadiene rubber.

The polymerizations of this invention are normally carried out assolution polymerizations in an inert organic medium. However, theinitiator systems of this invention can also be utilized in bulkpolymerizations or vapor phase polymerizations. In any case, the vinylcontent of the rubbery polymer made is controlled by the amount ofmodifier present during the polymerization.

In solution polymerizations the inert organic medium which is utilizedas the solvent will typically be a hydrocarbon which is liquid atambient temperatures which can be one or more aromatic, paraffinic orcycloparaffinic compounds. These solvents will normally contain from 4to 10 carbon atoms per molecule and will be liquids under the conditionsof the polymerization. It is, of course, important for the solventselected to be inert. The term “inert” as used herein means that thesolvent does not interfere with the polymerization reaction or reactwith the polymers made thereby. Some representative examples of suitableorganic solvents include pentane, isooctane, cyclohexane, normal hexane,benzene, toluene, xylene, ethylbenzene and the like, alone or inadmixture. Saturated aliphatic solvents, such as cyclohexane and normalhexane, are most preferred.

The allylic lithium compounds that can be used are typically made byreacting an alkyl lithium compound with a conjugated diolefin monomer.The conjugated diolefin monomer will typically be 1,3-butadiene orisoprene. The benzylic lithium compounds that can be used are typicallymade by reacting an alkyl lithium compound with a vinyl aromaticmonomer, such as styrene or alpha-methyl styrene. The alkyl lithiumcompounds that can be used in making the allylic lithium or benzyliclithium compound can be represented by the formula: R—Li, wherein Rrepresents a hydrocarbyl radical containing from 1 to about 20 carbonatoms. Some representative examples of alkyllithium compounds which canbe employed include methyllithium, ethyllithium, isopropyllithium,n-butyllithium, sec-butyllithium, n-octyllithium, tert-octyllithium,n-decyllithium. Aryl lithium compounds, such as, phenyllithium,1-napthyllithium, 4-butylphenyllithium, p-tolyllithium,1-naphthyllithium, 4-butylphenyllithium, p-tolyllithium,4-phenylbutyllithium, cyclohexyllithium, 4-butylcyclohexyllithium, and4-cyclohexylbutyllithium, can also be used. Some representative examplesof preferred alkyllithium compounds that can be utilized includeethylaluminum, isopropylaluminum, n-butyllithium,secondary-butyllithium, and normal-hexyllithium. Normal-butyllithium andsecondary-butyllithium are highly preferred lithium initiators.

The allylic lithium compound or the benzylic lithium compound can bemade by continuously adding the conjugated diolefin monomer or the vinylaromatic monomer to a line containing a solution of the alkyl lithiumcompound. In such cases, the line will typically flow into the reactorto initiate polymerization. In the alternative, the allylic lithiumcompound or the benzylic lithium compound can be made by a batch processwherein the conjugated diolefin monomer or vinyl aromatic monomer isadded into a solution containing the alkyl lithium compound. In eithercase, the molar ratio of the alkyl lithium compound to the conjugateddiolefin monomer or vinyl aromatic monomer will be within the range of1:1 to 1:50. The molar ratio of the alkyl lithium compound to theconjugated diolefin monomer or vinyl aromatic monomer will preferably bewithin the range of 1:2 to 1:25. The molar ratio of the alkyl lithiumcompound to the conjugated diolefin monomer or vinyl aromatic monomerwill more preferably be within the range of 1:5 to 1:10.

The amount of lithium initiator utilized in the initiator systems ofthis invention will vary with the specific allylic lithium or benzyliclithium compound empolyed and with the molecular weight that is desiredfor the rubber being synthesized. As a general rule in all anionicpolymerizations, the molecular weight (Mooney viscosity) of the polymerproduced is inversely proportional to the amount of lithium utilized. Asa general rule, from about 0.01 phm (parts per hundred parts by weightof monomer) to 1 phm of the lithium catalyst will be employed. In mostcases, from 0.01 phm to 0.1 phm of the lithium catalyst will be employedwith it being preferred to utilize 0.025 phm to 0.07 phm of the lithiumcatalyst.

Normally, from about 5 weight percent to about 35 weight percent of themonomer will be charged into the polymerization medium (based upon thetotal weight of the polymerization medium including the organic solventand monomer). In most cases, it will be preferred for the polymerizationmedium to contain from about 10 weight percent to about 30 weightpercent monomer. It is typically more preferred for the polymerizationmedium to contain from about 20 weight percent to about 25 weightpercent monomer.

The polymerization temperature will normally be within the range ofabout 5° C. to about 120° C. For practical reasons and to attain thedesired microstructure the polymerization temperature will preferably bewithin the range of about 20° C. to about 80° C. Polymerizationtemperatures within the range of about 40° C. to about 70° C. are morepreferred with polymerization temperatures within the range of about 55°C. to about 65° C. being the very most preferred.

The polymerization is allowed to continue until essentially all of themonomer has been exhausted. In other words, the polymerization isallowed to run to completion. Since a lithium catalyst is employed topolymerize the monomer, a living polymer is produced. The living polymersynthesized will have a weight average molecular weight of at least300,000. The high vinyl polymer synthesized will typically have a weightaverage molecular weight that is within the range of about 350,000 toabout 2,000,000. The rubber synthesized will more typically have aweight average molecular weight that is within the range of about400,000 to about 1,000,000.

To increase the level of vinyl content the polymerization is carried outin the presence of at least one polar modifier. Ethers and tertiaryamines which act as Lewis bases are representative examples of polarmodifiers that can be utilized. Some specific examples of typical polarmodifiers include diethyl ether, di-n-propyl ether, diisopropyl ether,di-n-butyl ether, tetrahydrofuran, dioxane, ethylene glycol dimethylether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether,diethylene glycol diethyl ether, triethylene glycol dimethyl ether,trimethylamine, triethylamine, N,N,N′,N′-tetramethylethylenediamine,N-methyl morpholine, N-ethyl morpholine, N-phenyl morpholine and thelike.

The modifier can also be a 1,2,3-trialkoxybenzene or a1,2,4-trialkoxybenzene. Some representative examples of1,2,3-trialkoxybenzenes that can be used include1,2,3-trimethoxybenzene, 1,2,3-triethoxybenzene, 1,2,3-tributoxybenzene,1,2,3-trihexoxybenzene, 4,5,6-trimethyl-1,2,3-trimethoxybenzene,4,5,6-tri-n-pentyl-1,2,3-triethoxybenzene,5-methyl-1,2,3-trimethoxybenzene, and 5-propyl-1,2,3-trimethoxybenzene.Some representative examples of 1,2,4-trialkoxybenzenes that can be usedinclude 1,2,4-trimethoxybenzene, 1,2,4-triethoxybenzene,1,2,4-tributoxybenzene, 1,2,4-tripentoxybenzene,3,5,6-trimethyl-1,2,4-trimethoxybenzene,5-propyl-1,2,4-trimethoxybenzene, and3,5-dimethyl-1,2,4-trimethoxybenzene. Dipiperidinoethane,dipyrrolidinoethane, tetramethylethylene diamine, diethylene glycol,dimethyl ether and tetrahydrofuran are representative of highlypreferred modifiers. U.S. Pat. No. 4,022,959 describes the use of ethersand tertiary amines as polar modifiers in greater detail.

The utilization of 1,2,3-trialkoxybenzenes and 1,2,4-trialkoxybenzenesas modifiers is described in greater detail in U.S. Pat. No. 4,696,986.The teachings of U.S. Pat. No. 4,022,959 and U.S. Pat. No. 4,696,986 areincorporated herein by reference in their entirety. The microstructureof the repeat units which are derived from butadiene monomer is afunction of the polymerization temperature and the amount of polarmodifier present. For example, it is known that higher temperaturesresult in lower vinyl contents (lower levels of 1,2-microstructure).Accordingly, the polymerization temperature, quantity of modifier andspecific modifier selected will be determined with the ultimate desiredmicrostructure of the polybutadiene rubber being synthesized being keptin mind.

The Group I metal alkoxides that is used in the initiator system of thisinvention will typically contain a Group I metal selected from the groupconsisting of lithium, sodium, potassium, rubidium, and cesium. TheGroup I metal alkoxide can be a compound of the formula M-O—R, wherein Mrepresents the Group I metal and wherein R represents an alkyl groupcontaining from 1 to about 20 carbon atoms. U.S. Pat. No. 5,654,384 andU.S. Pat. No. 5,906,956 disclose a number of sodium alkoxide compoundsthat can be used in the practice of this invention. The teaching of U.S.Pat. No. 5,654,384 and U.S. Pat. No. 5,906,956 are incorporated hereinby reference with respect to the types of sodium alkoxide compounds thatcan be used.

The Group I metal alkoxide will preferably be a metal salt of the cyclicalcohol. Lithium, sodium, potassium, rubidium, and cesium salts arerepresentative examples of such salts with lithium, sodium, andpotassium salts being preferred. Sodium salts are typically the mostpreferred. The cyclic alcohol can be mono-cyclic, bi-cyclic ortri-cyclic and can be aliphatic or aromatic. They can be substitutedwith 1 to 5 hydrocarbon moieties and can also optionally containhetero-atoms. For instance, the metal salt of the cyclic alcohol can bea metal salt of a di-alkylated cyclohexanol, such as2-isopropyl-5-methylcyclohexanol or 2-t-butyl-5-methylcyclohexanol.These salts are preferred because they are soluble in hexane. Metalsalts of disubstituted cyclohexanol are highly preferred because theyare soluble in hexane and provide similar modification efficiencies tosodium t-amylate. Sodium mentholate is the most highly preferred metalsalt of a cyclic alcohol that can be empolyed in the practice of thisinvention. Metal salts of thymol can also be utilized. The metal salt ofthe cyclic alcohol can be prepared by reacting the cyclic alcoholdirectly with the metal or another metal source, such as sodium hydride,in an aliphatic or aromatic solvent.

The Group I metal alkoxide to the polar modifier will normally be withinthe range of about 0.1:1 to about 10:1 and the molar ratio of Group Imetal alkoxide to the lithium initiator will normally be within therange of about 0.01:1 to about 20:1. It is generally preferred for themolar ratio of the Group I metal alkoxide to the polar modifier to bewithin the range of about 0.2:1 to about 5:1 and for the molar ratio ofthe Group I alkoxide to the lithium initiator to be within the range ofabout 0.05:1 to about 10:1. It is generally more preferred for the molarratio of the Group I metal alkoxide to the polar modifier to be withinthe range of about 0.5:1 to about 1:1 and for the molar ratio of theGroup I metal alkoxide to the lithium initiator to be within the rangeof about 0.2:1 to about 3:1.

After the polymerization has been completed, the living rubbery polymercan optionally be coupled with a suitable coupling agent, such as a tintetrahalide or a silicon tetrahalide. The rubbery polymer is thenrecovered from the organic solvent. The polydiene rubber can berecovered from the organic solvent and residue by any means, such asdecantation, filtration, centrification and the like. It is oftendesirable to precipitate the rubbery polymer from the organic solvent bythe addition of lower alcohols containing from about 1 to about 4 carbonatoms to the polymer solution. Suitable lower alcohols for precipitationof the rubbery polymer from the polymer cement include methanol,ethanol, isopropyl alcohol, normal-propyl alcohol and t-butyl alcohol.The utilization of lower alcohols to precipitate the rubber from thepolymer cement also “kills” the living polymer by inactivating lithiumend groups. After the rubbery polymer is recovered from the solution,steam stripping can be employed to reduce the level of volatile organiccompounds in the polymer. The inert solvent and residual monomer canthen be recycled for subsequent polymerization.

There are valuable benefits associated with utilizing the high vinylpolydiene rubbers made with the initiator systems of this invention intire tread compounds. These benefits include excellent tractioncharacteristics, low hysteresis and better functionalization effeciency.The high vinyl polydiene rubber will have at least 50 percent repeatunits that are of vinyl microstructure based upon the total number ofpolydiene repeat units in the rubbery polymer. The high vinylpolybutadiene rubber has a weight average molecular weight of at least300,000, wherein said high vinyl polybutadiene rubber has a monomodalpolydispersity of at least 1.2, and a ratio of radius of gyration toweight average molecular weight of greater dun 0.078 nm·mol/kg, whereinthe radius of gyration is determined at the weight average molecularweight by multi angle laser light scattering and wherein the weightaverage molecular weight is determined by multi angle laser lightscattering. The high vinyl polydiene rubber will typically have amonomdal polydispersity of at least 1.3.

The high vinyl polydiene rubber will preferably have a vinyl content ofat least 55 percent and a monomodal polydispersity of at least 1.4. Thehigh vinyl polydiene rubber will also preferable have a ratio of radiusof gyration to weight average molecular weight of greater than 0.08nm·mol/kg. The high vinyl polydiene rubber will more preferable have aratio of radius of gyration to weight average molecular weight ofgreater than 0.082 nm·mol/kg.

It is, of course, possible to blend the high vinyl rubber with otherrubbery polymers, such as natural rubber, synthetic polyisoprene rubber,cis-1,4-polybutadiene rubber, medium vinyl polybutadiene rubber,conventional solution styrene-butadiene rubber, emulsionstyrene-butadiene rubber, or conventional styrene-isoprene-butadienerubber, in making useful tire tread compounds.

The high vinyl polydiene rubber can be compounded utilizing conventionalingredients and standard techniques. For instance, the polybutadienerubber blends will typically be mixed with carbon black and/or silica,sulfur, fillers, accelerators, oils, waxes, scorch inhibiting agents,and processing aids. In most cases, the high vinyl polydiene rubberblend will be compounded with sulfur and/or a sulfur containingcompound, at least one filler, at least one accelerator, at least oneantidegradant, at least one processing oil, zinc oxide, optionally atackifier resin, optionally a reinforcing resin, optionally one or morefatty acids, optionally a peptizer and optionally one or more scorchinhibiting agents. Such blends will normally contain from about 0.5 to 5phr (parts per hundred parts of rubber by weight) of sulfur and/or asulfur containing compound with 1 phr to 2.5 phr being preferred. It maybe desirable to utilize insoluble sulfur in cases where bloom is aproblem.

Normally from 10 to 150 phr of at least one filler will be utilized inthe blend with 30 to 80 phr being preferred. In most cases at least somecarbon black will be utilized in the filler. The filler can, of course,be comprised totally of carbon black. Silica can be included in thefiller to improve tear resistance and heat build up. Clays and/or talccan be included in the filler to reduce cost. The blend will alsonormally include from 0.1 to 2.5 phr of at least one accelerator with0.2 to 1.5 phr being preferred. Antidegradants, such as antioxidants andantiozonants, will generally be included in the tread compound blend inamounts ranging from 0.25 to 10 phr with amounts in the range of 1 to 5phr being preferred. Processing oils will generally be included in theblend in amounts ranging from 2 to 100 phr with amounts ranging from 5to 50 phr being preferred. The polybutadiene blends of this inventionwill also normally contain from 0.5 to 10 phr of zinc oxide with 1 to 5phr being preferred. These blends can optionally contain from 0 to 10phr of tackifier resins, 0 to 10 phr of reinforcing resins, 1 to 10 phrof fatty acids, 0 to 2.5 phr of peptizers, and 0 to 1 phr of scorchinhibiting agents.

In cases where silica is included in the tread rubber compound, theprocessing of the polydiene rubber blend is normally conducted in thepresence of a sulfur containing organosilicon compound to realizemaximum benefits. Examples of suitable sulfur containing organosiliconcompounds are of the formula:Z-Alk-S_(n)-Alk-Z  (I)in which Z is selected from the group consisting of

where R¹ is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl;wherein R² is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8carbon atoms; and wherein Alk is a divalent hydrocarbon of 1 to 18carbon atoms and n is an integer of 2 to 8.

Specific examples of sulfur containing organosilicon compounds which maybe used in accordance with the present invention include:3,3′-bis(trimethoxysilylpropyl) disulfide,3,3′-bis(triethoxysilylpropyl) tetrasulfide,3,3′-bis(triethoxysilylpropyl) octasulfide,3,3′-bis(trimethoxysilylpropyl) tetrasulfide,2,2′-bis(triethoxysilylethyl) tetrasulfide,3,3′-bis(trimethoxysilylpropyl) trisulfide,3,3′-bis(triethoxysilylpropyl) trisulfide,3,3′-bis(tributoxysilylpropyl) disulfide,3,3′-bis(trimethoxysilylpropyl) hexasulfide,3,3′-bis(trimethoxysilylpropyl) octasulfide,3,3′-bis(trioctoxysilylpropyl) tetrasulfide,3,3′-bis(trihexoxysilylpropyl) disulfide,3,3′-bis(tri-2″-ethylhexoxysilylpropyl) trisulfide,3,3′-bis(triisooctoxysilylpropyl) tetrasulfide,3,3′-bis(tri-t-butoxysilylpropyl) disulfide, 2,2′-bis(methoxy diethoxysilyl ethyl) tetrasulfide, 2,2′-bis(tripropoxysilylethyl) pentasulfide,3,3′-bis(tricyclonexoxysilylpropyl) tetrasulfide,3,3′-bis(tricyclopentoxysilylpropyl) trisulfide,2,2′-bis(tri-2″-methylcyclohexoxysilylethyl) tetrasulfide,bis(trimethoxysilylmethyl) tetrasulfide, 3-methoxy ethoxy propoxysilyl3′-diethoxybutoxy-silylpropyltetrasulfide, 2,2′-bis(dimethylmethoxysilylethyl) disulfide, 2,2′-bis(dimethyl sec.butoxysilylethyl)trisulfide, 3,3′-bis(methyl butylethoxysilylpropyl) tetrasulfide,3,3′-bis(di t-butylmethoxysilylpropyl) tetrasulfide, 2,2′-bis(phenylmethyl methoxysilylethyl) trisulfide, 3,3′-bis(diphenylisopropoxysilylpropyl) tetrasulfide, 3,3′-bis(diphenylcyclohexoxysilylpropyl) disulfide, 3,3′-bis(dimethylethylmercaptosilylpropyl) tetrasulfide, 2,2′-bis(methyldimethoxysilylethyl) trisulfide, 2,2′-bis(methylethoxypropoxysilylethyl) tetrasulfide, 3,3′-bis(diethylmethoxysilylpropyl) tetrasulfide, 3,3′-bis(ethyldi-sec.butoxysilylpropyl) disulfide, 3,3′-bis(propyldiethoxysilylpropyl) disulfide, 3,3′-bis(butyl dimethoxysilylpropyl)trisulfide, 3,3′-bis(phenyl dimethoxysilylpropyl) tetrasulfide, 3-phenylethoxybutoxysilyl 3′-trimethoxysilylpropyl tetrasulfide,4,4′-bis(trimethoxysilylbutyl) tetrasulfide,6,6′-bis(triethoxysilylhexyl) tetrasulfide,12,12′-bis(triisopropoxysilyl dodecyl) disulfide,18,18′-bis(trimethoxysilyloctadecyl) tetrasulfide,18,18′-bis(tripropoxysilyloctadecenyl) tetrasulfide,4,4′-bis(trimethoxysilyl-buten-2-yl) tetrasulfide,4,4′-bis(trimethoxysilylcyclohexylene) tetrasulfide,5,5′-bis(dimethoxymethylsilylpentyl) trisulfide,3,3′-bis(trimethoxysilyl-2-methylpropyl) tetrasulfide,3,3′-bis(dimethoxyphenylsilyl-2-methylpropyl) disulfide.

The preferred sulfur containing organosilicon compounds are the3,3′-bis(trimethoxy or triethoxy silylpropyl) sulfides. The mostpreferred compound is 3,3′-bis(triethoxysilylpropyl) tetrasulfide.Therefore as to formula I, preferably Z is

where R² is an alkoxy of 2 to 4 carbon atoms, with 2 carbon atoms beingparticularly preferred; Alk is a divalent hydrocarbon of 2 to 4 carbonatoms with 3 carbon atoms being particularly preferred; and n is aninteger of from 3 to 5 with 4 being particularly preferred.

The amount of the sulfur containing organosilicon compound of formula Iin a rubber composition will vary depending on the level of silica thatis used. Generally speaking, the amount of the compound of formula Iwill range from about 0.01 to about 1.0 parts by weight per part byweight of the silica. Preferably, the amount will range from about 0.02to about 0.4 parts by weight per part by weight of the silica. Morepreferably the amount of the compound of formula I will range from about0.05 to about 0.25 parts by weight per part by weight of the silica.

In addition to the sulfur containing organosilicon, the rubbercomposition should contain a sufficient amount of silica, and carbonblack, if used, to contribute a reasonably high modulus and highresistance to tear. The silica filler may be added in amounts rangingfrom about 10 phr to about 250 phr. Preferably, the silica is present inan amount ranging from about 15 phr to about 80 phr. If carbon black isalso present, the amount of carbon black, if used, may vary. Generallyspeaking, the amount of carbon black will vary from about 5 phr to about80 phr. Preferably, the amount of carbon black will range from about 10phr to about 40 phr. It is to be appreciated that the silica coupler maybe used in conjunction with a carbon black, namely pre-mixed with acarbon black prior to addition to the rubber composition, and suchcarbon black is to be included in the aforesaid amount of carbon blackfor the rubber composition formulation. In any case, the total quantityof silica and carbon black will be at least about 30 phr. The combinedweight of the silica and carbon black, as hereinbefore referenced, maybe as low as about 30 phr, but is preferably from about 45 to about 130phr.

The commonly employed siliceous pigments used in rubber compoundingapplications can be used as the silica. For instance the silica caninclude pyrogenic and precipitated siliceous pigments (silica), althoughprecipitate silicas are preferred. The siliceous pigments preferablyemployed in this invention are precipitated silicas such as, forexample, those obtained by the acidification of a soluble silicate,e.g., sodium silicate.

Such silicas might be characterized, for example, by having a BETsurface area, as measured using nitrogen gas, preferably in the range ofabout 40 to about 600, and more usually in a range of about 50 to about300 square meters per gram. The BET method of measuring surface area isdescribed in the Journal of the American Chemical Society, Volume 60,page 304 (1930).

The silica may also be typically characterized by having adibutylphthalate (DBP) absorption value in a range of about 100 to about400, and more usually about 150 to about 300. The silica might beexpected to have an average ultimate particle size, for example, in therange of 0.01 to 0.05 micron as determined by the electron microscope,although the silica particles may be even smaller, or possibly larger,in size.

Various commercially available silicas may be considered for use in thisinvention such as, only for example herein, and without limitation,silicas commercially available from PPG Industries under the Hi-Siltrademark with designations 210, 243, etc; silicas available fromRhone-Poulenc, with, for example, designations of Z1165MP and Z165GR andsilicas available from Degussa AG with, for example, designations VN2and VN3.

Tire tread formulations which include silica and an organosiliconcompound will typically be mixed utilizing a thermomechanical mixingtechnique. The mixing of the tire tread rubber formulation can beaccomplished by methods known to those having skill in the rubber mixingart. For example the ingredients are typically mixed in at least twostages, namely at least one non-productive stage followed by aproductive mix stage. The final curatives including sulfur vulcanizingagents are typically mixed in the final stage which is conventionallycalled the “productive” mix stage in which the mixing typically occursat a temperature, or ultimate temperature, lower than the mixtemperature(s) than the preceding non-productive mix stage(s). Therubber, silica and sulfur containing organosilicon, and carbon black ifused, are mixed in one or more non-productive mix stages. The terms“non-productive” and “productive” mix stages are well known to thosehaving skill in the rubber mixing art. The sulfur vulcanizable rubbercomposition containing the sulfur containing organosilicon compound,vulcanizable rubber and generally at least part of the silica should besubjected to a thermomechanical mixing step. The thermomechanical mixingstep generally comprises a mechanical working in a mixer or extruder fora period of time suitable in order to produce a rubber temperaturebetween 140° C. and 190° C. The appropriate duration of thethermomechanical working varies as a function of the operatingconditions and the volume and nature of the components. For example, thethermomechanical working may be for a duration of time which is withinthe range of about 2 minutes to about 20 minutes. It will normally bepreferred for the rubber to reach a temperature which is within therange of about 145° C. to about 180° C. and to be maintained at saidtemperature for a period of time which is within the range of about 4minutes to about 12 minutes. It will normally be more preferred for therubber to reach a temperature which is within the range of about 155° C.to about 170° C. and to be maintained at said temperature for a periodof time which is within the range of about 5 minutes to about 10minutes.

Tire tread compounds made using such high vinyl polydiene rubber blendscan be used in tire treads in conjunction with ordinary tiremanufacturing techniques. Tires are built utilizing standard procedureswith the high vinyl polydiene rubber blend simply being substituted forthe rubber compounds typically used as the tread rubber. After the tirehas been built with the high vinyl polydiene rubber containing blend, itcan be vulcanized using a normal tire cure cycle. Tires made inaccordance with this invention can be cured over a wide temperaturerange. However, it is generally preferred for the tires to be cured at atemperature ranging from about 132° C. (270° F.) to about 166° C. (330°F.). It is more typical for the tires of this invention to be cured at atemperature ranging from about 143° C. (290° F.) to about 154° C. (310°F.). It is generally preferred for the cure cycle used to vulcanize thetires to have a duration of about 10 to about 20 minutes with a curecycle of about 12 to about 18 minutes being most preferred.

This invention is illustrated by the following examples which are merelyfor the purpose of illustration and are not to be regarded as limitingthe scope of the invention or the manner in which it can be practiced.Unless specifically indicated otherwise, all parts and percentages aregiven by weight.

EXAMPLES Materials and Methods

Materials.—Butadiene and styrene were supplied by The Goodyear Tire &Rubber Company, and was freshly distilled and degassed with nitrogenprior to use. Hexane was supplied by Ashland Chemicals and purified bypassing over an activated bed of silica gel under a dry nitrogenatmosphere. N-butyllithium (n-BuLi) was supplied by Chemetall Inc. andwas used as received. TMEDA was purchased from Aldrich and was used asreceived. SMT was supplied by The Goodyear Tire & Rubber Company.

Polymerizations.—Batch polymerizations were conducted in a 3.8 literreactor. The reactor was equipped with a variable speed agitator and aheating/cooling coil to control the reactor temperature via adistributed Foxboro control system. A representative procedure forconducting a polymerization was to first fill the reactor with hexaneand pickle with 1.5 ml of 1.6M n-BuLi solution at 65° C. The pickledhexane was then dumped from the reactor and the reactor was blown downwith dry nitrogen for two minutes to purge any residual liquid.Approximately 1500 grams of 15 weight percent styrene-butadiene (25/75weight percent) solution in hexanes was charged into the reactor. Thereactor temperature was then brought to its set point of 65° C., and apredetermined amount of modifier and n-BuLi was charged into the reactorusing a syringe via the injection port on the reactor. The reaction thencommenced and samples of the reaction mixture were taken via a diplegduring the course of polymerization for residual monomer analysisutilizing gas chromatography (GC). The GC results were used to calculatemonomer conversions in order to determine whether monomers reach theirfull conversions.

Characterization.—Size-exclusion chromatography (SEC) was performedusing a Wyatt Technologies miniDawn light scattering detector coupledwith a Hewlett Packard 1047A refractive index detector. PolymerLaboratories B, C, and D mixed microgel columns were utilized withtetrahydrofuran as the carrier solvent at a flow rate of 0.35 ml/min anda column temperature of 40° C. Sample preparation involved filtering a0.12 weight percent solution of polymer in THF through a 1.0 μm filterprior to injection. Polystyrene standards were used to calibrate theinstrument.

Results and Discussion

The initiation in anionic polymerization is always assumed to be afaster step compared to propagation, and the initiator n-BuLi wasimmediately consumed. Instant initiation may be assumed in batchpolymerization and in plug flow reactor processes. In a continuousprocess, the reactants and products constantly flow into and out of thereactor. Theoretically, every species exists in the reactor at any giventime due to the reactor residence time distribution. Therefore, in atypical butadiene-styrene copolymerization system, three reactivespecies, i.e. two propagating species of allylic lithium(butadienyllithium) and benzylic lithium (styryllithium) and initiatorn-BuLi may be present. In the presence of polar modifiers, these threereactive species may exhibit different metallation strengths. It is thusimportant to distinguish their individual metallation strength for anyprocess improvement aimed at reducing the polymer branching.

A. Preparation of Butadienyllithium and Styryllithium

To isolate the effects of different reactive species, butadienyllithium(allylic lithium) and styryllithium (benzylic lithium) species have tobe prepared. Preformed butadienyllithium was prepared through thereaction of butadiene and n-butyllithium. In a 4-oz oven-dried nitrogenpurged bottle, 50 grams of 15 weight percent butadiene solution inhexanes was charged into the bottle. Using a syringe, 17.4 ml of 1.6Mn-BuLi was added into the bottle to pre-form an allylic lithiuminitiator with the molar ratio of butadiene to n-BuLi being 5:1. Thebottle was placed in 65° C. water bath and tumbled for 30 minutes.

Styryllithium cannot be prepared directly through the reaction ofn-butyllithium and styrene in hexane because oligomer of styrene willprecipitate from the hexane solution. A two-step procedure was thusdesigned in this study to form a soluble styryllithium. First butadieneoligomers were prepared by reacting butadiene with n-butyllithium asdescribed in the preparation of butadienyllithium. After the livingbutadienyl oligomer was preformed, a test polymerization was conductedto check the active concentration of butadienyllithium. Based upon theGPC result and the amount of butadiene from the test polymerization, theactive concentration was determined. A soluble form of benzylic lithiumwas then formed by adding 2 molar equivalents of styrene to the livingbutadienyl oligomers.

B. Metallation Method

Anionic systems using heavy alkali metal alkoxides have been a researchtopic for many years. The majority of studies were designed to identifythe resulting metallating species and to understand the operatingmechanism, while polymerization was neglected (see Modrini, A., Adv.Carbanion Chem., 1992, 1, 1; Lochmann, L.; Trekoval, J. Collect. Czech.Chem. Comm., 1988, 15, 585; Lochmann, L.; Lim, D., J. Organomet. Chem.,1971, 28, 153; and Pi, R.; Bauer, B.; Schade, C.; Schleyer, P. v. R., J.Organomet. Chem., 1986, 306, C1). In practice, the polymerization systemis complicated by many factors such as counter-cations and the additionof polar modifiers. In particular, multiple active lithium species arepresent in a copolymerization system and in the polymerization processeach reactive species may possess different metallating strengths towarda polymer backbone. In addition, polymer chain propagation, metallation,and subsequent monomer addition occur concurrently. It is thus essentialto isolate these events to investigate the metallation mechanism of asingle reactive species.

In U.S. Pat. No. 5,562,310, a procedure was described to metallate thepolymer chain and prepare grafted copolymers. In the disclosed method,it assumed that the additional n-BuLi was all consumed to metallate theterminated polymer backbone and additional monomer was all grafted onthe polymer backbones resulting in chain branching. Using a similarapproach, Kerns and Henning (see Kerns, M. L. and Henning, S. K.,Presented at the Deutsche Kautschuk Tagung Meeting, September 2000)studied alkyllithium metallation with different counter-cations inbutadiene polymerization in the presence of TMEDA and sodium mentholate.They concluded that the mechanism of metallation reactions involve amulti-component complex.

In the current study, a similar three-step approach as used by Kerns andHenning was adopted to investigate the metallation strength of differentreactive species that are present in a continuous polymerizationprocess. First, a SBR rubber cement (i.e., base polymer) with 25 weightpercent styrene was prepared. The molecular weight of this base polymerwas targeted around 250,000 to 300,000 g/mol. This molecular weight ishigh enough to ensure a clean separation of the polymer formed insubsequent reaction. Upon the completion of the reaction, astoichiometric amount of ethanol was added into the reactor to terminatethe living polymer chains. The second step was to metallate theterminated polymer chains by adding a pre-determined amount ofco-modifiers and initiator with the ratios as described in Tables 1 and2. This reaction lasted about 45 minutes. Finally, an additional monomersolution (same as that used in the first step) was charged into thereactor to propagate the polymerization. The freshly charged monomer wasallowed to react until full conversion was achieved. The reaction wasthen terminated by injecting a small amount of ethanol and the finalpolymer was analyzed by SEC.

A typical SEC plot before and after the second monomer addition is shownin FIG. 1. The distribution with a single peak represents the basepolymer made in the first step. Final polymer shows a bimodaldistribution resulting from the mixture of polymers formed from thefirst step and the 3rd step. It is evident that a clean separation afterthe second monomer addition can be achieved.

The polymer chains formed after metallation were intentionally targetedat a lower molecular weight than base polymer formed in the first stepso that a clean separation based upon elution time on SEC can beachieved. Thus, the amount of polymers associated with the differentorigins could be determined. That is, additional monomer added after themetallation step could be consumed only in two ways: one is to form newpolymer chains with lower molecular weight than the base polymer,another is to be grafted onto the base polymer chains that weremetallated. The amount of polymer associated with these two differentorigins can be estimated based upon the areas under the peaks. Bycomparing with the amount of monomers charged into the reactor fromthese two different steps, the amount of monomer grafted onto the basepolymer chains can be calculated. The metallation strength can becorrelated the amount of additional monomer grafted onto the basepolymers. If a larger amount of additional monomer was found to begrafted onto the base polymer, the initiator system exhibits strongermetallation power.

C. Metallation Strength of Alkyllithium, Allylic Lithium and BenzylicLithium

Using the aforementioned metallation method, a set of experiments wasdesigned to study the metallation strength of n-BuLi, butadienyllithium,and styryllithium under the mixed modifier system consisting of TMEDAand sodium mentholate. The results were summarized in Table I. Basepolymer molecular weight and its polydispersity (1^(st) addition) arelisted in the 3^(rd) and 4^(th) columns (labeled in the table under thecolumn headings). After the second monomer addition, the molecularweight and its distribution of base polymer were changed due to themonomer grafted onto the backbone and their values are listed in the5^(th) and 6^(th) columns. Any newly formed polymer had much lowermolecular weight than the base polymer and its Mw and polydispersity aregiven in the 8^(th) and 9^(th) columns. The 7^(th) and 10^(th) columnsgive the estimated weight percentage of the polymers from the molecularweight distribution curves corresponding to the base polymer and newlyformed polymer, respectively. The theoretical weight fraction of newpolymer was calculated based upon the amount of monomer charged into thereactor and was listed in the 11^(th) column. This value is calculatedassuming no metallation occurred. The amount of monomer charged into thereactor after the metallation step that was then attached onto the basepolymer chains was calculated and listed in the last column(12^(th)).

To highlight the difference of metallation strength associated with thethree initiators, the data in the last column in Table I was re-groupedto reflect the different initiator systems in the metallation step andwas plotted in FIG. 2.

From the Table I and FIG. 2, it is observed that 1.) when allyliclithium and benzylic lithium initiators were used in the metallationstep, the monomer added after metallation was mostly consumed in theformation of new polymer chains, no matter what the modifiercombination; 2.) more than half of the additional monomer was grafted onthe base polymer when n-BuLi was used in the metallation step; and 3)the metallation strength of the initiator system is greatly enhancedeven with small amounts of sodium mentholate are present in the process(A-2).

TABLE I BATCH METALLATION EXPERIMENTS 1^(st) addition Post 2^(nd)addition Base Polymer Base Polymer New polymer Theor. Mw Mw Amt Mw Amtamt Grafted* 2^(nd) addition (kg/mol) Mw/Mn (kg/mol) Mw/Mn (wt %)(kg/mol) Mw/Mn (wt %) (wt %) (wt %) Expt Ratio 3rd 4th 5th 6th 7th 8th9th 10th 11th 12th 2^(nd) addition initiator system: TMEDA/SMT/n-BuLiA-1 3.0/0.0/1.0 221.8 1.06 293.6 1.11 92.1 70.25 1.31 7.9 21.31 62.9 A-20.0/0.1/1.0 244.8 1.05 275.1 1.12 88.7 67.12 1.28 11.4 20.32 44.1 A-33.0/0.1/1.0 241.5 1.05 292.1 1.16 91.2 62.39 1.38 8.8 20.32 56.6 2^(nd)addition initiator system: TMEDA/SMT/Allylic lithium B-1 3.0/0.0/1.0244.8 1.05 257.2 1.05 90.4 34.33 1.38 9.65 9.43 −2.3 B-2 0.0/0.1/1.0232.0 1.05 235.3 1.05 71.9 21.95 1.23 28.1 26.5 −6.1 B-3 3.0/0.1/1.0309.0 1.07 314.8 1.12 91.0 65.2 1.01 8.97 9.35 4.0 2^(nd) additioninitiator system: TMEDA/SMT/Styryllithium C-1 3.0/0.0/1.0 345.3 1.02343.7 1.06 77.6 37.45 1.28 22.4 23.45 4.5 C-2 0.0/0.1/1.0 244.5 1.06250.3 1.06 79.2 25.87 1.15 20.8 20.94 0.7 C-3 3.0/0.1/1.0 239.6 1.05234.4 1.1 79.3 28.0 1.30 20.7 21.0 1.4 *the amount of monomer that wasgrafted onto the base polymers based upon the additional monomer chargedinto the reactor after metallation

Earlier studies (see Falk, J. C.; Schlott, R. J.; Hoeg, D. F.;Pendleton, J. F. Rubber Chem. Tecnol., 1973, 46, 1044; and Tate, D. P.;Halasa, A. F.; Webb, F. J.; Koch, R. W.; Oberster, A. E. J. Polym.Sci.:Part A-1, 1971, 9, 139) demonstrated that the TMEDA/n-BuLi systemwould metallate diene-based polymers. However, a recent study by Kernsand Henning¹³ did not find that significant metallation occurred intheir system, albeit under different conditions. The current study (A-1)showed that substantial metallation did occur in this system with over60 wt % of the additional monomer being grafted onto the base polymerchains. Based upon these findings, it is concluded that the metallationstrength would follow the order of alkyllithium being stronger thanallylic lithium with is equivalent to benzylic lithium.

Although little metallation was found when allylic lithium and benzyliclithium were used in the current study, our unpublished plant trial datashow that branching increases from the first reactor to the secondreactor when the modifier combination of TMEDA/SMT is used. This seemsto be in contradiction to the concept and the above finding thatmetallation only occurs when alkyllithium is present in the reactor. Itis believed that there is no or very little free alkyllithium presenceafter the first reactor in a continuous process due to the rapidinitiation in a highly modified system. To resolve this, we investigatedthe effect of temperature on the extent of metallation using allyliclithium as an initiator. The results are summarized in Table II underthe same column format as explained for Table I. The data in the lastcolumn in Table II was plotted in FIG. 3.

TABLE II TEMPERATURE EFFECT ON BATCH METALLATION 1^(st) addition Post2^(nd) addition Base Polymer Base Polymer New polymer Theo. MetallationMw Mw Amt Mw Amt amt Grafted* Expt Temp (° C.) (kg/mol) Mw/Mn (kg/mol)Mw/Mn (wt %) (kg/mol) Mw/Mn (wt %) (wt %) (wt %) 2^(nd) additioninitiator system: TMEDA/SMT/allylic lithium = 3.0/0.1/1.0 B-3 65 309.01.07 314.8 1.12 91.03 65.2 1.01 8.97 9.35 4.0 D-2 72 260.0 1.04 263.21.12 80.2 33.49 1.34 19.8 22.62 12.5 D-3 78 279.0 1.06 286.8 1.30 83.039.69 1.25 17.0 23.56 27.8 *the amount of monomers was grafted onto thebase polymers based upon the additional monomer charged into the reactorafter metallation.

It is clear that the extent of metallation increases with the reactiontemperature and the amount of monomer grafted onto the base polymermonotonically increases. It is therefore not surprising that the degreeof branching will be higher after the first reactor in a continuousprocess if higher temperatures are employed in the later reactors

D. Practical Examples

To confirm the above finding, two continuous experiments were designedto prepare high vinyl SBRs using mixed modifiers of TMEDA and SMT (TableIII). The continuous process contains two reactors. In Experiment 1,initiator n-BuLi was directly fed into the first reactor. Reactortemperatures in both reactors were kept at 85° C. As seen in subsectionC, alkyllithium exhibits a much stronger metallation tendency thanallylic lithium or styryllithium. In Experiment 2, to eliminate thepossible existence of n-BuLi in the reactor, a preformed allylic lithiumwas prepared when n-BuLi (chain extended n-BuLi with butadiene) waspre-reacted with 10 butadiene units and the resulting oligomer was thenfed into the reactor. Reactor temperatures in both reactors weremaintained at 75° C. to minimize metallation and branching reactions.The characterization data of the polymers synthesized in these twoexperiments are summarized in Table III.

TABLE III CHARACTERIZATION OF CONTINUOUS POLYMERS Sample Type Polymer aPolymer b Method to Pre-formed Direct Feed initiator Mooney (OE), 37.552.7 53.0 phr Gerstine Oil, ML₁₊₄, 100° C. Molecular Weight distributionMn, g/mol 380,100 465,000 Mw, g/mol 545,300 809,100 Polydispersity 1.441.74 Radius Gyration Rn, nm 40.3 45.4 Rw, nm 45.9 53.2 Branching levelRw/Mw, nm-mol/kg 0.0842 0.0658 M-DSC Tg (onset, OE), ° C. −28.8 −21.4

As described in the paper of Kerns and Henning, Size ExclusionChromatography (SEC) with Multi Angle Laser Light Scattering (MALLS) canbe used to determine the relative level of branching by comparing theradius of gyration at a given molar mass. Since branched polymerexhibits a smaller coil size compared to its linear counterpart, theradius gyration will be smaller at a given molecular weight (see Bauer,B. J.; Fetters, L. J., Rubber Chemistry and Technology, 1978, 51, 406).

FIG. 4 shows the root mean square radius as a function of molar mass forthe high vinyl SBR samples. It is seen that both samples give a similarradius at low molar masses. At higher weights, polymer b with n-BuLibeing directly fed into the reactor has a much smaller radius at highmolecular weights, indicating a relatively higher branching level in thepolymer.

It is known that linear and branched polymers show different linearviscoelastic response under simple oscillatory shear flow. Branchedpolymers typically exhibit higher Newtonian viscosity at low shear ratesdue to their increased relaxation time and entanglements caused by thebranching points. Dynamic testing with a constant stress parallel platerheometer has been demonstrated to adequately characterize the low shearrate behavior of polymers by extending the test to low angularfrequencies so that it allows the polymer sample to reach the plateauand terminal zone behavior (see Bauer, B. J.; Fetters, L. J., RubberChemistry and Technology, 1978, 51, 406).

Branched polymers normally show higher G′ values at low angularfrequencies because their increased physical entanglements confine themovement of polymer chains and the external deformation can betransferred into the elastic component of moduli. It was also found thatthe crossover frequency of elastic and loss shear modulus (G″ overtakesG′) correlates well with the level of branching given the samemicrostructure and molecular weight. FIG. 5 shows G′ and G″ behavior ofboth samples as a function of frequency. It is observed that there iscrossover for polymer a at the frequency of 0.4 rad/sec while nocrossover occurred for polymer b in the frequency range the measurementwas conducted. This implies that there are indeed more branching pointsalong the backbone of polymer a than there are in polymer b, even thoughboth polymers exhibit similar mooney viscosities. An alternative way toreflect the relative branching level is the dependency of tan delta(G″/G′) on frequency. The lower the value of tan delta, the morebranched polymer will be. FIG. 6 shows that the polymer a has muchhigher values of tan delta than that of polymer b. Moreover, polymer aexhibits crossover (tan Δ=1.0), while polymer b does not have. All ofthese means that polymer a have more linear macrostructure than polymerb. This is consistent with the analysis and results from theaforementioned metallation study

E. Compound Properties

A standard silica formation with 86 phr Rhodia Zeosil 1165 was used withBR/sSBR at a 30/70 phr ratio. The BR used in the formulation was Budene®1207 high cis-polybutadiene rubber. The primary interest of this studyis to demonstrate the benefit of in-situ initiator technology. The datafrom the compounding evaluation is summarized in Table IV. Asaforementioned, the in-situ initiator technology will reduce the extentof metallation in our initiator system and thus lead to more linearpolymer. When this polymer is used in a tread compound formulation, itis expected to improve the hysteretic properties. It is evident fromTable IV that the hot rebound is higher for polymer b and Metravib tandelta value at 50° C. is much lower than that of polymer a, even thoughpolymer a has a slightly higher mooney viscosity.

TABLE IV HYSTERETIC ANALYSIS OF HIGH VINYL SBRs Sample Type Polymer aPolymer b Compounded Money 40.1 42.8 Shore A 66.9 64.8 Goodyear-HealeyRebound Cold Rebound (%) 8.8 8.6 Hot Rebound (%) 56.8 59.8 Metravib Tand (50° C., 6%) 0.2679 0.2079 Tan d (−10° C., 1.5%) 0.819 0.838

A Metallation study using different initiators combined with mixedmodifier of TMEDA and sodium mentholate has been conducted in batchexperiments. It is concluded that the metallation strength for differentinitiators follows the order of alkyllithium being greater than allyliclithium which is equivalent to styryllithium. Reaction temperature wasalso investigated with the selection of allylic lithium and thecombination of TMEDA and sodium mentholate as the modifier system. Itwas found that the metallation strength increases significantly with thetemperature.

The results from the batch experiments were used to guide the design ofan initiator feed system in a continuous process to minimize themetallation tendency inherent to the highly modified reaction systemthat is necessary to produce polymer materials with high vinyl contentand high glass transition. The compounding evaluation demonstrated thatthe in-situ initiator technology does lead to lower branching level inthe polymer sample and thus the hysteretic properties in a silicaformulation were significantly improved.

Variations in the present invention are possible in light of thedescription of it provided herein. It is, therefore, to be understoodthat changes can be made in the particular embodiments described whichwill be within the full intended scope of the invention as defined bythe following appended claims.

1. A high vinyl polydiene rubber which is comprised repeat units thatare derived from at least one conjugated diene monomer and afunctionalized monomer, wherein at least 50 percent of the repeat unitsare of vinyl microstructure based upon the total number of diene repeatunits in the rubbery polymer, wherein said high vinyl polydiene rubberhas a weight average molecular weight of at least 300,000, wherein saidhigh vinyl polydiene rubber has a monomodal polydispersity of at least1.3, and a ratio of radius of gyration to weight average molecularweight of greater than 0.078 nm·mol/kg, wherein the radius of gyrationis determined at the weight average molecular weight by multi anglelaser light scattering and wherein the weight average molecular weightis determined by multi angle laser light scattering.
 2. A rubberypolymer as specified in claim 1 wherein the functionalized monomer is ofthe structural formula:

wherein n represents the integer
 6. 3. A high vinyl polydiene rubber asspecified in claim 1 wherein the ratio of the radius of gyration toweight average molecular weight of the high vinyl polydiene rubber isgreater than 0.08 nm·mol/kg.
 4. A high vinyl polydiene rubber asspecified in claim 1 wherein the high vinyl polydiene rubber has aweight average molecular weight that is within the range of about400,000 to about 1,000,000.
 5. A high vinyl polydiene rubber asspecified in claim 4 wherein the high vinyl polydiene rubber has a vinylmicrostructure content of at least 55 percent.
 6. A high vinyl polydienerubber as specified in claim 5 wherein the ratio of the radius ofgyration to weight average molecular weight of the high vinyl polydienerubber is greater than 0.082 nm·mol/kg.
 7. A high vinyl polydiene rubberas specified in claim 6 wherein the monomodal polydispersity of the highvinyl polydiene rubber is at least 1.4.
 8. A high vinyl polydiene rubberas specified in claim 2 wherein the high vinyl polydiene rubber has aweight average molecular weight that is within the range of about350,000 to about 2,000,000.
 9. A high vinyl polydiene rubber asspecified in claim 5 wherein the polydiene repeat units in the highvinyl polydiene rubber are derived from 1,3-butadiene and wherein thehigh vinyl polydiene rubber is high vinyl polybutadiene rubber.
 10. Ahigh vinyl polydiene rubber as specified in claim 5 wherein thepolydiene repeat units in the high vinyl polydiene rubber are derivedfrom isoprene and wherein the high vinyl polydiene rubber is3,4-polyisoprene rubber.
 11. A high vinyl polydiene rubber as specifiedin claim 9 wherein the repeat units in the high vinyl rubber are furtherderived from a vinyl aromatic monomer.
 12. A high vinyl polydiene rubberas specified in claim 11 wherein the vinyl aromatic monomer is styreneand wherein the high vinyl polydiene rubber is styrene-butadiene rubber.